FARS2 deficiency; new cases, review of clinical, biochemical, and molecular spectra, and variants interpretation based on structural, functional, and evolutionary significance

Mol Genet Metab. 2018 Nov;125(3):281-291. doi: 10.1016/j.ymgme.2018.07.014. Epub 2018 Jul 29.


An increasing number of mitochondrial diseases are found to be caused by pathogenic variants in nuclear encoded mitochondrial aminoacyl-tRNA synthetases. FARS2 encodes mitochondrial phenylalanyl-tRNA synthetase (mtPheRS) which transfers phenylalanine to its cognate tRNA in mitochondria. Since the first case was reported in 2012, a total of 21 subjects with FARS2 deficiency have been reported to date with a spectrum of disease severity that falls between two phenotypes; early onset epileptic encephalopathy and a less severe phenotype characterized by spastic paraplegia. In this report, we present an additional 15 individuals from 12 families who are mostly Arabs homozygous for the pathogenic variant Y144C, which is associated with the more severe early onset phenotype. The total number of unique pathogenic FARS2 variants known to date is 21 including three different partial gene deletions reported in four individuals. Except for the large deletions, all variants but two (one in-frame deletion of one amino acid and one splice-site variant) are missense. All large deletions and the single splice-site variant are in trans with a missense variant. This suggests that complete loss of function may be incompatible with life. In this report, we also review structural, functional, and evolutionary significance of select FARS2 pathogenic variants reported here.

Keywords: Epileptic encephalopathy; FARS2; Mitochondria; Mitochondrial aminoacyl-tRNA synthetase; Spastic paraplegia.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Amino Acyl-tRNA Synthetases / deficiency
  • Amino Acyl-tRNA Synthetases / genetics*
  • Child
  • Child, Preschool
  • Female
  • Gene Deletion
  • Humans
  • Male
  • Mitochondria / enzymology
  • Mitochondria / genetics*
  • Mitochondria / pathology
  • Mitochondrial Diseases / enzymology
  • Mitochondrial Diseases / genetics*
  • Mitochondrial Diseases / pathology
  • Mitochondrial Proteins / chemistry
  • Mitochondrial Proteins / deficiency
  • Mitochondrial Proteins / genetics*
  • Mutation / genetics
  • Paraplegia / genetics
  • Paraplegia / pathology
  • Phenylalanine / genetics
  • Phenylalanine / metabolism
  • Phenylalanine-tRNA Ligase / chemistry
  • Phenylalanine-tRNA Ligase / deficiency
  • Phenylalanine-tRNA Ligase / genetics*
  • Protein Isoforms / genetics
  • Structure-Activity Relationship
  • Young Adult


  • Mitochondrial Proteins
  • Protein Isoforms
  • Phenylalanine
  • Amino Acyl-tRNA Synthetases
  • FARS2 protein, human
  • Phenylalanine-tRNA Ligase